The Guardian has come under fire in Britain over its reporting on intelligence matters

Pierre Omidyar, founder of online auction site eBay, said Wednesday he is teaming up with journalist Glenn Greenwald, who has led reporting on secret U.S. surveillance programs, to create a new online mass media venture.

Greenwald announced late Tuesday that he was quitting The Guardian for "a once-in-a-career dream journalistic opportunity" but said he was not ready to give more details.

Now Omidyar has confirmed to CNN's Christiane Amanpour that he is behind the new media venture, which includes Greenwald and others -- and that he will personally fund it.

Greenwald has been at the forefront of a series of high-profile reports based on leaks from former U.S. National Security Agency contractor Edward Snowden.

Journalist Jeremy Scahill and documentary filmmaker Laura Poitras will also be joining the venture, Omidyar said.

Greenwald has been working with Poitras, based in Berlin, on NSA-related stories. Scahill is the author of the New York Times best-seller "Blackwater: The Rise of the World's Most Powerful Mercenary Army."

Greenwald, who lives in Brazil, said Tuesday that it had not been easy to leave The Guardian, but that he could not turn down the "momentous new venture."

"My partnership with the Guardian has been extremely fruitful and fulfilling: I have high regard for the editors and journalists with whom I worked and am incredibly proud of what we achieved," he said.

"The decision to leave was not an easy one, but I was presented with a once-in-a-career dream journalistic opportunity that no journalist could possibly decline. "

The Guardian's Jennifer Lindauer said Greenwald was a "remarkable journalist" and that it had been "fantastic" to work with him.

"Our work together over the last year has demonstrated the crucial role that responsible investigative journalism can play in holding those in power to account," she said. "We are of course disappointed by Glenn's decision to move on, but can appreciate the attraction of the new role he has been offered. We wish him all the best."

The Guardian has come under fire in recent days from figures in the UK intelligence community who suggest its reporting has undermined efforts to keep the country safe in the face of terror threats.

Both Greenwald and The Guardian have accused UK authorities of using heavy-handed tactics to try to silence legitimate reporting.

Greenwald's partner, David Miranda, was detained for hours by UK authorities at London's Heathrow Airport in mid-August, as he was changing planes en route to the couple's Rio de Janeiro home. Items including a laptop, a hard drive and USB memory sticks were confiscated from him and are the subject of a legal challenge.

Greenwald said the episode was designed to deter him and other investigative journalists from using classified information and digging into stories critical of the British and allied governments -- but vowed to continue regardless.

Guardian editor Alan Rusbridger described meetings with UK government officials who demanded the newspaper hand over the Snowden material or destroy it.

A week ago, the head of Britain's MI5 security service, Andrew Parker, used his first public speech to say that reporting on the work of Britain's intelligence agency, Government Communications Headquarters, risks handing over vital information to terrorists.

"It causes enormous damage to make public the reach and limits of GCHQ techniques," he said.

"Such information hands the advantage to the terrorists. It is the gift they need to evade us and strike at will. Unfashionable as it might seem, that is why we must keep secrets secret, and why not doing so causes such harm."

Parker did not name The Guardian or Snowden in his comments but said that the information gleaned about terrorists and "the detail of the capabilities we use against them" was what gave intelligence services their "margin of advantage" -- a margin, he said, that is now "under attack."

A former head of GCHQ and adviser to 10 Downing Street, Sir David Omand, also last week said in an interview with The Times of London that leaks by Snowden of intelligence documents represent "the most catastrophic loss to British intelligence ever."